Field of the Invention
This invention relates to the field of stereolithography, which is a technique for making solid, three-dimensional objects (or "parts") from solidifiable materials (e.g. fluid or fluid-like material such as photopolymers, sinterable powders, and bindable powders).
In recent years, stereolithography systems, such as those described in U.S. Pat. No. 4,575,330, issued Mar. 11, 1986 and entitled "Apparatus for Production of Three-Dimensional Objects by Stereolithography," have come into use. Basically, stereolithography is a method for automatically building complex three-dimensional parts by successively solidifying thin cross-sectional layers. These layers may be composed of photopolymer resin, powdered materials, or the like. Some types of powder materials are converted from a fluid-like medium to a cohesive cross-section by melting and solidification. The layers are solidified on top of each other consecutively until all of the thin layers are joined together to form a whole part. Photocurable polymers change from liquid to solid upon exposure to synergistic stimulation. Many photopolymers exist whose photospeed (rate of transformation from liquid to solid) upon irradiation with ultraviolet light (UV) is fast enough to make them practical model building materials. In a preferred system, a radiation source (e.g., an ultraviolet laser) generates a beam which is focused to a small intense spot which is moved across the liquid photopolymer surface by galvanometer or servo type mirror x-y scanners. The scanners are driven by computer generated vectors or the like. The material that is not polymerized when a part is made is still functionable and remains in the vat for use as successive parts are made. With this technology, the parts are literally grown from a vat of fluid-like material (e.g. resin or powder). Specifically, the parts are grown from a thin layer near a surface of the vat of fluid-like material. In this manner precise complex three dimensional patterns can be rapidly produced. This method of fabrication is extremely powerful for quickly reducing design ideas to physical form for making prototypes.
This technology typically utilizes a stereolithography apparatus, referred to as an "SLA," which generally includes a laser and scanner, a photopolymer vat, an elevator, and a controlling computer. The SLA is programmed to automatically make a three-dimensional part by forming it as a sequence of built-up cross-sectional layers.
Stereolithography represents an unprecedented way to quickly make complex or simple parts without tooling. Since this technology depends on using a computer to generate its cross-sectional patterns, there is a natural data link to computer aided design and manufacture (CAD/CAM). However, such systems have presented challenges relating to structural stress, shrink-age, curl and other distortions, as well as resolution, speed, accuracy and difficulties in producing certain object shapes.
The techniques to be described herein are also useful in other Solid Modeling, or Rapid Prototyping and Manufacturing, technologies. One of these other technologies builds up objects from sheets of materials, as described in U.S. patent application Ser. No. 07/803,681, now U.S. Pat. No. 5,182,715. In some embodiments these sheets of material are transformed upon exposure to appropriate radiation, which transformation can benefit from the techniques to be described herein.